The unusual swimmer stunned fishermen who said they never saw bears venturing so far out to sea.

A brown bear swimming this far out to sea is very unusual but cases like this one have been recorded by scientists. Picture: Kam24

The predator was filmed crossing the bay from its northern to southern side towards the closed city of Vilyuchinsk, one of Russian nuclear submarine bases.

A man who filmed the bear nor far from the bay’s ‘gate’ into the ocean is heard saying to the animal: ‘Hey man, where are you swimming?! The water is cold and it’s the middle of the bay! ’

A brown bear swimming this far out to sea is very unusual but cases like this one have been recorded by scientists, said experts from the Kronotsky Nature Reserve.

‘Bears are outstanding swimmers. Water temperature is never an issue for them as their pelt and layer of fat protects them. We have history of brown bears swimming as far as 11 kilometres’, said reserve’s science department consultant Alexander Nikonorov.

He said however that the reasons why bears venture out swimming big distances have not been studied yet.

The video has also been watched by experts of Kamchatka regional forestry agency and department for wildlife protection.

They suggested that the bear’s most likely destination was the southern bank of the bay, home to closed city of Vilyuchinsk.

Avacha Bay is a Pacific Ocean bay on the southeastern coast of the Kamchatka Peninsula.

Avacha Bay. Pictures: 2r.ru, Dmitry Ovechkin

It is 24 km long and 3 km wide, with a maximum depth of 26 metres.

The Avacha River flows into the bay.

The port city of Petropavlovsk-Kamchatsky and the closed town of Vilyuchinsk lie on the coast of the bay.